Method of making metallic magnesium



Patented June 7, 1932 UN lTE DSTA TES PATENT: ol-rlcla RALPH M. HUNTERAND SHELDON B. HEATH, F MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICALCOMPANY, MIGBIGAN Nomawing.

The present invention concerns a method of producing metallic magnesiumby the electrolysis of a fused bath containing mag-' essary to replenishthe bath and maintain it of the desired character by feeding thereto 16an equivalent of the magnesium and chlorine or other essentialingredients which, in the course of operations, have been or may-beremoved therefrom.

It is well known that the ideal feed to such 20 a cell comprisesanhydrous MgGl and that accompanying water will reduce the current andpower efliciency of electrolysis. It is further known that inertconstituents of the feed, such as MgO, tend to settle out of the bath,and unless removed therefrom, will accumulate and interfere withcontinuous operation. Such sediment must accordingly be removed, whichis customarily done by dredging from time to time as re uired, but thisoperation removes also part 0 the bath along with the sediment orso-called sludge. In practice we have found that as high as twoequivalents of bath may be removed in that way with one uivalent ofsludie figured as MgO. The bat so removed wit the sludge must, ofcourse, be returned by feeding to the cell the constituents so removedin addition to that required to replenish the MgCl converted to metaland chlorine.

Anhydrous MgCl is not only difiicult and expensive to prepare, but onaccount of its hygroscopic properties it is practically impossible tohandle it without its taking up some moisture, and in practice, acontent of 95 per cent MgCl in the chloride fed to the cell isconsidered obtainable good practice.-

In U. S. Patent No. 1,567,318 is disclosed a method of feeding MgClcontaining water, whereby the detrimental effects of the water '0 areminimized.

or MIDLAND, moment, a coaroan'rron or un'rnon or name METALLIC menasruuApplication mm m 27, 1929. Serial 110.886,!518.

In the copending application Serial No. 280,659, there is disclosed bySheldon B. Heath, co-inventor herein, a method of utilizing magnesiumchloride containing basic Itghlglride to replenish and maintain thefused We have discovered an improved method of introducing the MgCl fedto such an electrolytic cell having marked advantage as contrasted withmethods heretofore disclosed or known to us, said improved method beingap plicable to introduction of MgCl containing water orsimilarintroduction of MgCl containing basic salt.-

To the accomplishment of the foregoing and related ends, the invention,then, consists of the. steps hereinafter fully described and aparticularly pointed out in the claim, the following description settingforth in detail one approved mode of carrying out our invention.

It has heretofore been customary to introduce the feed at one point inthe cell and in accordance with the patent application referred toabove, adjacent the anode. Such method of feeding gave improved resultsover previous practice 'on a relatively small scale, but when cells oflarge capacity were used, particularly cells employing a plurality ofanodes which in certain cases may be distributed relative to a largebath area," that method of feeding was foundto produce large quantitiesof sludge, to involve over-cooling of the bath locally at the point offeed introduction, and to localize anode wear. The removal of thisexcessive quantity of sludge entailed the removal therewith of increasedquantities of bath requiring increased added feed to maintain the bath,such feed carrying with it more basic salt or water or both, therebyadding still further to the sludge formation.

-We have now discovered that if the cell feed including MgCl containingbasic salt or water or both be fed to the cell in a manner to distributeit relative to the active anode surface, a smaller amount of sludge isformed, local cooling of the bath is substantially avoided and the anodewear is distributed more evenly. The dredging is correspond- 100 inglyreduced as is. the loss of bath therewith and what is most important therequirement for feed is'likewise markedly reduced. The mechanics ofthephenomenon of reduced sludge production are not definitely lmown.

It may be that thedistributed mode offeeding permits the solution in thebath of the face instead of allowing it to fall to the bottom of thebath where it becomes inert basic chloride adjacent "the activeanode surand that the so dissolved basic salt is reacted upon by CO and chlorineto form M 1 CO and HCl. Whatever the cause 0 the said phenomenon theimproved method of introducing the feed constitutes a valuableimprovement in the art.

' 1 of the feed relative to the anode surface is to f A simple method ofattaining distribution introduce said feed at a number of points insteadof at one point. a The size, character and form of the cell willnaturally determine the exact method of introduction and the number ofpoints at'which' introduction may advisably be made, but very markedimprovement is attained-by introducin at even but two points in a cellof upwa-r of 10000 ampere capacity m t still further improvement 1 thestepor steps stated by the may be expected by introducing such feed atmore than two points,.the feed being in troduced in a fairly continuousmanner.

We have found further that good results may be thus obtained when usinga feed carrying as low or lower than 5 er cent equivalent MgO byintroducing it into the bath at other points than adjacent the anode,

but we prefer, particularly with feeds running higher than 5 per centequivalent MgO content, to introduce same adjacent the anode distributedrelative to the anode surface. Other modes of applying the principle ofour invention may be em loyed instead of the one explained, change beingmade as regards the-method herein disclosed, fprovided ollowin-g claimor the equivalent of such stated step or steps be employed. 7

We therefore particularly point out and distinctly claim as ourinvention e In the production of metallic magnesium by electrolyzing amolten bath containing magnesium chloride, wherein the raw mate-' rialfed tosaid bath consists of magnesium chloride containing some water orbasic chlo.

ride, the improvement which consists in feed ing such raw materialtosaid bath adjacent the anode at a plurality of points distributed withreference to the anode surface.

Signed by us this 23rd day of Ma 1929. RALPH M. HUNT R.

SHELDON B. HEATH.

